A semiconductor laser has a wide range of applications, such as an optical disk apparatus, a laser beam printer, a copy machine, etc. High speed performance and high capability of information processing are typically required for the semiconductor laser applications. To meet the requirements for high speed performance and high capability of information processing, there has been proposed a so-called multi-beam semiconductor laser apparatus which emits a plurality of laser beams (hereinafter referred to as a “multi-beam”) as a source of light.
Such a multi-beam semiconductor laser apparatus has a structure where stripe semiconductor laser devices are arranged in the form of a plurality of arrays to emit light. Thus, the plurality of semiconductor laser devices is used to generate and emit laser light.
In the multi-beam semiconductor laser apparatus, for the purpose of independently driving the laser devices, separation grooves for electrical isolation between the laser units are formed between adjacent laser units. The respective laser units have wiring layers to connect stripe electrodes formed on a ridge having its sides surrounded by the separation grooves, and pad electrodes formed away from the ridge. As density and integration of the apparatus becomes larger, a distance between adjacent laser devices becomes smaller resulting in an electrical crosstalk between the laser devices.
There is, for example, a technique for reducing electrical crosstalk by forming high resistive separation regions between the laser emission units and between the laser emission units and conductive layers acting as lead units.
However, conventional multi-beam semiconductor laser apparatuses have problems of thermal crosstalk in addition to the electrical crosstalk. A thermal crosstalk refers to heat generated by current applied to one semiconductor laser unit, which has an effect on different semiconductor laser units, such that power from laser beams of individual semiconductor laser units may be varied. For example, inner laser units, which are arranged in parallel are more likely to store heat than outer ones, which may result in an increase of temperature of the apparatus and, hence, deterioration of crosstalk characteristics.
In addition, the wiring distance of the inner laser devices from pad electrodes in the conventional multi-beam semiconductor laser apparatus is longer than that of the outer ones. Thus the resistance of the inner laser devices is larger than that of the outer ones by the amount corresponding to the difference in the wiring distance. This has an effect on laser driving current and the amount of heat generated and may result in poor emission characteristics of the inner laser devices, which are farther away from the pad electrodes than the outer ones.